Social networks can influence people through contagion. what does that mean?

This implies when individuals are associated with an informal organization, what occurs in that system will probably influence them. 
Sociologists allude to the networks of immediate and backhanded binds interfacing people to other people who impact them as Social Network. The humanist Duncan Watts analyzed the way that people may alter their opinions about who to vote in favor of in view of the suppositions of companions and associates.